Soil exposed to large quantities of chemicals such as wood preserving chemicals, petroleum products, manufactured gas plant wastes and the like may become contaminated with chlorophenols, volatile organic compounds and polycyclic aromatic hydrocarbons (PAHs). Pentachlorophenol (PCP), a substance commonly used as a wood preservative or pesticide, and other chlorinated phenolic compounds become associated with the soil when released into the environment. Because these substances are considered toxic chemicals, a process for successfully and efficiently reducing the amount of PCP and PAHs in soil to acceptable levels is desired.
Biological degradation is one method currently employed in the treatment of PAHs and PCP contaminated soils. This method relies upon microorganisms in the soil to degrade the PCP and PAHs. However, biological degradation is a slow and time consuming process. The toxicity of the contaminants, recalcitrance of the target chemicals, and the slow rate of diffusion of the PCP and/or PAHs carrying non-aqueous phase liquid through the soil matrix can interfere with the degradation process. Moreover, the microorganisms require specific soil conditions, such as the availability of required nutrients, the oxygen and moisture content in the soil, and the soil pH.
Photodegradation or photolysis is another method of reducing contaminants through the absorption of light energy and the use of the absorbed energy to break chemical bonds. PCP in aqueous solution has been degraded by exposing the solution to ultraviolet radiation. However, photodegradation of PCP in soil is more difficult because the light required to degrade the contaminants typically has a penetration depth of less than 0.3 mm, essentially limiting photolysis to the contaminants in the surface layer of the soil. The use of solvents such as ethanol to extract the contaminants from the soil and carry the contaminants to the soil surface has been studied. P. C. Ellis, Treatment of Pentachlorophenol (PCP) Contaminated Soil Using Indigenous Biological Degradation and Photodegradation, 1995, M.S. Thesis, Utah State University, Logan, Utah; M. A. Cooley, Treatment of Pentacholorphenol (PCP)-Contaminated Soil Using Enhanced Unsaturated Flow and Photodegredation, 1994, M.S. Thesis, Utah State University, Logan, Utah. In the processes studied in the theses, ethanol was injected into the bottom of a pan without saturating the soil and allowed to migrate upwardly through the contaminated soil through capillary action. The soil was exposed to light for photodegration of the contaminants carried to the soil surface by the ethanol. While this process showed satisfactory results compared to biodegradation processes in the laboratory, degradation of the contaminants occurred at a significantly slower rate when this process was employed in the field.
A process of efficiently and quickly reducing the amount of contaminants in soil is desirable. A process which may be used to degrade contaminants when employed in the field, allowing the contaminated soil to be treated in both a time-efficient and cost-efficient manner, is also desirable.